Semifree-ranging Tufted Capuchins (Cebus apella) Spontaneously Use Tools to Crack Open Nuts

Naturalistic studies on tool use by nonhuman primates have focused almost exclusively on Old World monkeys or hominoids. We studied the cracking of Syagrus nuts with the aid of stones by a group of semifree-ranging capuchins living in a reforested area (Tietê Ecological Park, São Paulo, Brazil). Our data are from direct observation and from mapping nut-cracking site utilization. All adults, subadults and juveniles (plus one infant) crack nuts, but individual differences in frequency and proficiency are marked. Juveniles do most of the nut-cracking, but adults are, on average, more efficient; the frequency of inept stone manipulation decreases with age. About 10% of the nut-cracking episodes were watched by other individuals—mostly infants and juveniles, suggesting a role for observational learning, even if restricted to stimulus enhancement.     

The mental arms race amplifier

The use of tools to obtain food is probably a long-standing hominid adaptation. Therefore, the rapid increase in hominid brain size over the last million years cannot be explained by selection for basic tool use alone. Two alternative theories, here termed the ecological adaptation hypothesis and the intraspecific competition hypothesis, are reviewed and rejected. Instead, a combination of these two theories is offered: the mental arms race amplifier hypothesis.     

A clarification of Pouydebat et al., 2008, evolution of grasping among anthropoids

Several statements by Pouydebat et al. (2008) do not adequately represent views of authors cited, in part because they reflect confusion in the literature about terminology regarding precision gripping. We address these problems, by tracing definitions of precision grips through the literature on manipulative behaviour and identifying the grip that is central to the Pouydebat et al. (2008) study. This allows us to offer a clarification of the statements by Pouydebat et al. (2008) regarding the sequence of appearance of human grip capabilities and possible morphological correlates to these capabilities in extant species.     

Transfer of tools and food between groups of tufted capuchins (Cebus apella)

This research examined tool and food transfer between two groups of tufted capcuhin monkeys (Cebus apella). Subjects in one group transferred stones to subjects in a second group who in turn used the stones as cutting tools and then transferred food to subjects in the first group. Aspects of the capuchins' behavior are similar to those described for food-sharing in Cebus, cooperative tool use in Papio, and tool and food exchange in Pan. We propose that tool use and food-sharing facilitate tool and food transfer between captive groups of Cebus apella. Am. J. Primatol. 43:33–41, 1997. © 1997 Wiley-Liss, Inc.     

The subsistence technology of capuchins

Via Oswalt’s system of classification, I compare the tool-kits of wild and captive capuchins with those of Tanzanian chimpanzees and Tasmanian aborigines. The results indicate that capuchins have tool-kits that are smaller, and have lower ratios of artifacts to naturefacts, than those of Tanzanian chimpanzees and Tasmanian aborigines. Accordingly, Oswalt’s system can be used productively to assess the relative technological skills of monkeys versus those of apes and humans.     

Effects of manipulatable objects on the activity of captive capuchin monkeys (Cebus apella)

The aim of this study was to evaluate simple behavioral enrichment procedures for a captive group of tufted capuchin monkeys (Cebus apella). We examined the effects of providing a manipulatable substrate (straw) and a variety of portable objects in the monkeys' home cage. The animals were observed across three conditions in two replications: 1) No portable objects were present; 2) a set of six identical portable objects was present; and 3) a set of six varied portable objects was present. The cage floor was bare in the first replication; straw was uniformly spread on the cage floor in the second replication. An 18-month period of qualitative note taking followed completion of the initial data collection phase. The presence of straw and portable objects affected patterns of affiliation by decreasing quiet contact and close proximity. Providing additional manipulative opportunities affected both the form and frequency of object-directed activities. Object contacts were directed toward a greater variety of targets, and some objects were spontaneously used as tools. Manipulation of provided objects and use of objects as tools have become routine activities in this group of monkeys. We conclude that providing straw and portable objects in an already well equipped cage is an effective means of long-term behavioral enrichment for captive capuchin monkeys. Enabling captive capuchins to express species-typical manipulative tendencies is apparently conducive to the monkeys' optimal physical and psychological well-being as well as interesting to the human observer.